Question

Work function of Cu metal is 4.8 eV. What is the approximate wavelength of incident radiation required to eject electrons from its surface? ($h = 6.626 \times 10^{-34}$ Js)

• A. 500 nm
• B. 450 nm
• C. 400 nm
• D. 258 nm

Hint:

To eject electrons, use $\lambda = \dfrac{hc}{\phi}$ where $\phi$ is in joules.

Answer 1

The Correct Option is D

Work function $\phi = 4.8$ eV = $4.8 \times 1.6 \times 10^{-19}$ J = $7.68 \times 10^{-19}$ J
Using: $\phi = \dfrac{hc}{\lambda} \Rightarrow \lambda = \dfrac{hc}{\phi}$
Substitute: $h = 6.626 \times 10^{-34}$ Js, $c = 3 \times 10^8$ m/s
$\lambda = \dfrac{6.626 \times 10^{-34} \cdot 3 \times 10^8}{7.68 \times 10^{-19}} = 2.58 \times 10^{-7}$ m = 258 nm